The danger of exposure to chemical or biological agents can be severe. Whether a result of unintended release, by way of, e.g., an accident, or intentional delivery, it is desirable to quickly and accurately identify (1) the type of agent that has been released and (2) the precise area of contamination. Early and accurate detection of such dangerous substances can be a significant factor in reducing potential casualties and limiting further spreading of the agent, e.g., by wind, human and animal contact, etc.
In recent years, there has been an increased interest in developing and deploying nuclear, biological, and chemical (NBC) sensor technologies to quickly identify unknown substances, contaminants, and agents, even at very low concentrations. Prior technologies designed to measure surface-deposited chemical contamination used vehicles and associated test equipment that retrieved a physical sample of the contaminant and then used an extremely cumbersome and time-consuming process based on a mechanical sampling wheel system to test for chemical agents.
In view of the complexity of such approaches, newer, simpler technologies were desired. One emerging technology in response to this desire is referred to, generally, as “standoff surface detection,” and refers to a category of technologies that permit detection of a substance without actually having to physically come in contact with the substance. The goal of these detection systems is to provide the capability to detect, identify, locate, quantify, warn, and report chemical and biological threats and thereby give military forces or civilian personnel sufficient early warning to avoid (further) contamination.
One of the technologies that enables standoff surface detection is Raman spectrometry. Raman spectrometry is a technique used to characterize materials and thereafter to identify such materials. Typically, a laser transmitter serves as a spectrally narrow light source with high irradiance. The laser illuminates a known or an unknown substance, such as chemical compounds, biological agents, among others. A portion of the incident light is Raman scattered by the substance. This light is scattered in all spatial directions as well as shifted spectrally into several discrete wavelengths. These wavelength shifts correspond to unique vibrational energies associated with the molecular bonds in the substance.
In conventional Raman spectroscopy systems, the Raman scattered light is collected by a telescope and is coupled into a dispersive optical system. The telescope focuses the collected light onto, e.g., an optical fiber bundle. At the opposite end of the fiber bundle, individual fibers are oriented linearly to form an entrance slit for a grating-based spectrograph. An electro-optical detector array records the optical spectrum of the Raman scattered light. This spectrum serves as a “fingerprint” for the known or unknown substance. An analysis computer either stores the “fingerprint” along with information identifying the known substance, or more often, employs pattern-matching algorithms to identify the unknown substance from a spectral library of previously analyzed and “fingerprinted” substances.
Laboratory-based Raman spectrometry systems have been known for many years. Recently, portable Raman systems have become possible as a result of components that have decreased in size. A description of one such portable system can be found in U.S. Pat. No. 6,608,677, which is incorporated herein by reference. A backpack implemented man-portable Raman sensor has also recently been fielded by ITT (Wilmington, Del.). Aspects of that system are described in U.S. patent application Ser. No. 11/688,434, entitled Method, Apparatus and System for Rapid and Sensitive Standoff Detection of Surface Contaminants, and filed Mar. 20, 2007, which application is also incorporated herein by reference. Truck mounted Raman sensors have also been fielded to date. Reference may also be made to U.S. Pat. No. 6,788,407 for still further discussion of Raman spectrometry.
Notwithstanding these known systems, there remains a need to provide different forms of Raman sensors to meet the needs of both civilian and military personnel responsible for identifying and ultimately handling dangerous substances and items.